Ancient Light Caps Black Hole Mass
New analysis of the cosmic microwave background sets a 100 billion solar mass limit on dark matter black holes.
By Layla Edwards ·
The oldest light in the universe has settled a long-standing debate about the nature of dark matter.
Researchers have determined that black holes exceeding 100 billion solar masses cannot comprise a major portion of the invisible mass holding galaxies together. Dark matter is estimated to make up about five-sixths of all matter in the cosmos, yet its physical form remains unknown. Black holes have long been considered a plausible candidate due to their immense gravity and low visibility.
The study targets "stupendously large black holes," objects with masses ranging from 1 million to 10 million billion times that of the sun. Such massive bodies would outweigh entire galaxies, yet none have been detected to date. The largest known black hole weighs approximately 36 billion solar masses. Because these giant holes have not turned up in galaxy surveys, the team sought to verify if they could still constitute a substantial fraction of the total dark matter.
Christopher Gerlach, a theoretical physicist at the Mainz Institute for Theoretical Physics in Germany, explained that dark matter is typically imagined as a fine dust spread throughout space. He noted that if this mass were instead clumped into a few gigantic objects, the universe would appear grainy on very large scales. Gerlach stated that this graininess can be directly checked through observation.
The team analyzed the cosmic microwave background, a snapshot of the infant universe from 380,000 years after the Big Bang. At that time, the cooling of the plasma allowed light to travel freely. Antonio Iovino, a co-author at New York University Abu Dhabi, noted that the temperature of this background varies by about one part in 100,000 from place to place. This pattern reveals how matter was distributed in the early cosmos.
The analysis found no evidence of the graininess that would be caused by stupendously large black holes. Nicholas Leister, also of the Mainz Institute, concluded that these objects cannot be a significant part of the dark matter. The authors clarified that this result does not mean such black holes cannot exist, only that they are not a primary component. They are now investigating whether smaller, asteroid-sized black holes might account for the missing mass.
The findings are scheduled for publication in the journal Physical Review Letters on October 26.
Source: Space.com
